1. Field of the Invention
The present invention relates to the preparation of aldehydes, and, more especially, to the preparation of aldehydes by hydrocarbonylation of organic halides.
2. Description of the Prior Art
The hydrocarbonylation of organic halides has served as impetus for many investigations with a view to the development of an industrial process for the preparation of aldehydes. Thus, in Hungarian Pat. No. 150,412 (Chemical Abstracts, 60, 2847c) it has been recommended to effect hydrocarbonylation of organic halides (for example, octyl bromide and benzyl chloride) by reaction of the latter compounds with a mixture of carbon monoxide and hydrogen, under pressure, in the presence of dicobaltoctacarbonyl in an acetone/water mixture. Under these conditions the yields are often moderate and the reaction time on the order of 4 hours restricts the productivity of the process despite the use of high temperatures and pressures and a relatively large amount of catalyst.
In order to reduce the temperature and time of reaction it has been proposed, in French patent application No. 73/46,069, published under No. 2,211,451, and in Japanese patent application published under No. 75/149,610, to prepare phenylacetaldehyde and substituted derivatives thereof by hydrocarbonylation of benzyl halides in the presence of a catalyst consisting of a transition metal derivative, particularly dicobaltoctacarbonyl, in a water-immiscible organic solvent/water pair, said reaction being carried out in the added presence of a tertiary amide (dimethyl- or diethylformamide or acetamide) and a basic agent which serves to neutralize the hydrogen acid produced thereby (weak-acid salts of alkali metals or alkaline earth metals; alkali metal hydroxides; organic bases). Although the presence of the tertiary amide makes it possible to lower the temperature and to increase the yield of phenylacetaldehyde, the latter does not exceed 60% in the best of cases and the pressures employed remain high (on the order of 13.7 to 19.6 MPa). Furthermore, this process has the disadvantage of requiring the use of a large amount of amide (1 mole per mole of benzyl halide) and a still relatively high amount of catalyst (e.g., 0.26 mole of dicobaltoctacarbonyl per mole of benzyl halide).
In published European patent application No. 0,034,430 an attempt has been made to solve the problem of the hydrocarbonylation of arylmethyl halides to arylacetaldehydes by carrying out the reaction in a nitrile, optionally combined with a hydrocarbon, in the presence of a cobalt derivative and a base. The substitution of the nitrile/hydrocarbon system for the water-immiscible organic solvent/water system results in the production of good yields of arylacetaldehydes in the presence of small amounts of catalyst. Nevertheless, it is found that the reaction time remains on the order of 2 to 3 hours.
In capsule summary, despite the efforts carried out since the publication of Hungarian Pat. No. 150,412, serious industrial need continues to exist for a process for the preparation of aldehydes by hydrocarbonylation of organic halides which makes it possible to obtain both good yields of aldehydes and good productivity without requiring the use of a large amount of hydrocarbonylation catalyst and without resorting to high temperatures and/or pressures. Cf. U.S. Pat. No. 4,338,467; CA, 94, 46969s (1981).